It appears Katy Perry did not heed the Internet's advice to back away slowly from John Mayer. On the heels of their "sexy" dinner date last Wednesday at the Chateau Marmont, sources tell Wonderwall that the pair put on a public display of saliva swapping during a pool party on Saturday at a home in the Hollywood Hills.

"They were all over each other in the pool and were not being shy about it," an eyewitness tells us. "Katy had her legs wrapped around John in the water, and they were making out in front of everyone."

Concludes the spy, "They are clearly an item!"

The day after the pool-set tonsil-polishing, Katy, 27, was snapped entering the Four Seasons Hotel in Beverly Hills just a few minutes after John, 34, marking yet another sign that a hookup is afoot.

In addition to being spied "holding hands across the table" and locking lips while they dined at the Chateau (per Us), paparazzi caught the doll-faced popster being dropped off at her apartment the next morning in what appeared to be the crooner's Ferrari.

Two weeks earlier, Perry and Mayer reportedly rendezvoused at Soho House, where they once again fondled each other's fingers and cuddled up.

"I don't think either of them are trying for anything serious right now. She's not talking like he's The One," an insider explains to People. "She's comfortable around guys who understand the craziness of that world, which he definitely does."

But does he understand how to woo? Katy tells the September issue of Elle that she's "a woman who likes to be courted -- strongly."